The Needles Range Formation in Southwestern Utah: paleomagnetism and stratigraphic correlation

Extensive paleomagnetic and geologic investigation of the Needles Range Formation in southwestern Utah indicates there are three regional ash-flow tuff members: the Cottonwood Wash Tuff, the Wah Wah Springs Tuff, and the Lund Tuff. The paleomagnetic direction of the Wah Wah Springs Tuff is well defined with a declination of 181 and an inclination of -35. The other two regional tuffs have a less well defined normal magnetic direction. Local Needles Range Formation ash-flow tuffs are found in the area of the Sevier Plateau and at the WahWah Springs type section. The outcrop extent of the Formation is nearly a rectangle with dimensions 140 km north-south by 280 km east-west cen­ tered in southwestern Utah and extending 100 km into Nevada. Paleomagnetic and geologic techniques indicate a local Needles Range Ash-flow Tuff in the southern Sevier Plateau underwent auto-clastic brecciation subsequent to deposition and compaction. Limited downslope flowage is suggested as a possible brecciating mechanism. Extensive geologic and paleomagnetic investigation in the area of Clear Creek between the towns of Sevier and Cove Fort in central Utah reveal the Wah Wah Springs Tuff is within the Bullion Canyon Volcanics in that area. The Wah Wah Springs Tuff is preceeded by a local andesite flow and succeeded by a number of andesitic to rhyolitic flows and ash-flow tuffs, probably having their origin in the Tushar Mountains to the south. Previously unmapped faulting in this area is the site of partial release of stress caused by eastward tilting of the Pavant Range to the north and the Tushar Mountains to the south.